Alexander "Alex" Katsopolis (born November 12, 1991) is a fictional character on Full House (played by Kevin Renteria: season 5 and Dylan Tuomy-Wilhoit: seasons 6–8). He is the son of Jesse and Rebecca Katsopolis and identical twin brother of Nicky.
He grew up in the house with the Tanner family. Becky got pregnant with Alex and his twin brother Nicky and had trouble breaking the news to Jesse. She tries to tell him in a candlelight dinner but Jesse was too happy to go on tour. Later she told him in a game of Pictionary. On Michelle's birthday they had the twins. In "Nicky and/or Alexander", Jesse mixes them up by taking off their booties and put Alex's booties on Nicky. Later he inks Alex's foot. Then Becky finds out. He was named after Becky's teacher who gave her the inspiration to study journalism. He is blonde, has blue eyes, and wears red pajamas (as Michelle knew and Stephanie didn't in "The Perfect Couple").
Alex, much like Nicky, is a humorous and mischievous character. Throughout the seventh and eighth seasons, they caused trouble worth more than the two of them combined, let alone singular. They adore each other, which caused them to cling on each other until Jesse and Becky had them find their own personalities. They also were the focus of Jesse's attention and he tried to raise them the way that his own father never had, but it usually led to them overpowering him until Becky comes in with her motherly advice to him. Nevertheless, they are both still mischievous and cause much stress to their parents' lives.
- Rebecca Katsopolis (mother)
- Jesse Katsopolis (father)
- Nicky Katsopolis (brother)
- Danny Tanner (uncle)
- Pamela Tanner (aunt; deceased)
- D.J. Tanner (cousin)
- Stephanie Tanner (cousin)
- Michelle Tanner (cousin)
- Iorgos Katsopolis (great-grandfather)
- Gina Katsopolis (great-grandmother)
- Jackson Fuller (first cousin, once removed)
- Max Fuller (first cousin, once removed)
- Tommy Fuller Jr. (first cousin, once removed)
- Tommy Fuller, Sr. (cousin-in-law; deceased)
- Teri Tanner (step-aunt)
- Favorite animal: lion
- Nickname: Big Al
- Likes the color red
- Is right-handed
- In "Stephanie's Wild Ride", it is revealed that his favorite story is "Three Billy Goats Gruff".
- He and Nicky were born on Michelle's fifth birthday
- Since in the actor (Dylan) is older than his brother (Blake) by 19 minutes, it stands to reason that Alex is older than Nicky
After Full House ended he (and Nicky) graduated from high school. In Fuller House Nicky and Alex are in college, and open up a fish taco truck business together, after moving back in with Jesse and Becky. Nicky and Alex eventually become big brothers after Jesse and Becky adopt a baby girl.